The present disclosure relates to methods for processing steel coils in a cut-to-length and/or blanking line. The cut-to-length and/or blanking line will uncoil the sheet material, level it, and then cut it to the required length and stack it. The end product produced by a cut-to-length and/or blanking line is a flat sheet of material cut to a precise length tolerance.
As described in more detail below, in a cut-to-length and/or blanking line to level the coiled material, a stretcher leveler may be used or a temper mill may be used. Hot roll processing lines used to produce flat, stress-free sheets generally are two types, a stretcher leveler line or a temper mill line. The general description of a stretcher leveler is described in U.S. Pat. No. 4,751,838, which is incorporated herein by reference. The stretcher leveler stretches the material sufficiently to exceed the yield point in all the fibers of the strip from top to bottom and from edge to edge thus equalizing internal trapped stresses throughout the material. A stretcher leveler completes its work with usually only 0.3 to 0.5% elongation. The general description of a temper mill is described in U.S. Pat. No. 3,292,402, which is incorporated herein by reference. A temper mill eliminates randomly trapped internal stresses by elongating the material beyond its yield point by squeezing the material between two rolls with enough force to reduce its thickness. The typical amount of elongation in a temper mill is about 1 or 2%.
As described in more detail, the disclosure is directed to a processing line with both a temper mill and a stretcher leveler. The temper mill may be placed on-line and the stretcher leveler bypassed to process thin gage materials. Vice versa, the temper mill may be bypassed and the stretcher leveler may be placed on-line to process thicker gage material.
In one example, a small temper mill is integrated into a cut-to-length line having a stretcher leveler. The temper mill may be a 4 high or 2 high mill temper mill capable of handling coils having a gage thickness of between 16 gage (0.0598 inches) and 9 gage (0.1495). The temper mill may be configured to generate 75 kpsi maximum rolling stress and 2.5% elongation. The temper mill may be used to produce an improved surface finish and where there is concern for coil breaks. The temper mill may also provide increased production when compared to operations involved a stretcher leveler especially for thinner gages between 16 gage (0.0598 inches) and 9 gage (0.1495).
The stretcher leveler may be used for coils and/or sheets having a thickness of between 16 gage and ¾ inches. For the thicker sizes between 9 gage and ¾ inches, the slower speed of the stretcher leveler is not as critical since there is generally less warp in a thicker gage coil. The stretcher leveler may also be used for thin gage thickness coils, i.e. between 16 gage and 9 gage, having poor shape and/or where flatness is a concern.